This invention relates to an improved dual bank antenna. The invention allows the antenna to function with a radio wave transceiver in applications where the antenna must be compact and yet not be affected by the operator during use.
Portable radio equipment often uses electrically small or compact antennas which are located within the equipment housing. These prior antennas are subject to detuning and excessive loss which often occur when a high impedance part of the antenna is subject to close approach by the operator's hand or body. For example, short electric dipole or electric monopole antennas have the high impedance areas near the ends of the conductors, often the part of the antenna most exposed to interference by the operator's hand or body.
Another problem encountered by small or compact antennas is that the antenna gain varies inversely wtih the bandwidth. Increasing the gain decreases the bandwidth which significantly reduces the capability to transmit and receive signals. For example, loop antennas have a very narrow bandwidth and only a slight detuning will cause excessive loss, making the antenna highly inefficient.
Antennas for a miniature radio transceiver are known. One such an antenna having a low profile loop antenna structure for use when the radio is mounted on the operator's body and a high efficiency dipole antenna for use when the radio is held in the operator's hand is described in U.S. Pat. No. 4,313,119 to Oscar M. Garay and Kazimierz Siwiak, and assigned to Motorola, Inc., the assignee of the present invention. While that dual mode antenna is highly satisfactory for use with a two-way miniature radio or talk-back pager of the type worn on the body of a person, it is less satisfactory for use as portable radio equipment, such as cordless telephones.
It is therefore a general object of the present invention to provide a new and improved dual band transceiver antenna.
It is a further object of the present invention to provide such an antenna which is inductively loaded to be constructed in a compact size and promote high efficiency.
It is another object of the invention to provide an antenna which can be easily manufactured or fabricated using printed circuit techniques to produce the conductor pattern of the antenna.
It is still another object of the invention to provide an antenna with the high impedance field in the center of the antenna to minimize the detrimental effect that an operator can have upon the radio's performance.
It is a still further object of the invention to provide an improved antenna for a miniaturized transceiver including, a high Q parallel tuned circuit whereby said circuit "dual bands" the antenna.
It is still another object of the invention to provide an improved antenna for a compact transceiver wherein the antenna may be tuned to an exact frequency by a variable capacitor.